Studies are planned to examine cytotoxic responses of B-cells and T-cells (and their produce) in experimental Chagas' disease. Specifically, cytotoxic Ab and lymphocyte mediated cytotoxic (LMC) responses developed during the course of infection and/or to immunization will be monitored for destructive ability both quantitatively and qualitatively against the three forms of Trypanosoma cruzi. Indirect assay procedures for measuring these responses, including isotopic release procedures and terminal labeling assays, are being developed for quantification of these cytotoxic responses. Studies will be done comparing cytotoxic activity developed in C57BL/6J and C3H(He)Dub female mice during the course of the disease. C57 mice are significantly more resistant to T. cruzi infections than are C3H mice and experiments will be designed to determine the differences, if any, in specific cytotoxic responses between these animals. Evidence from these experiments could suggest the immunologic basis for resistance to T. cruzi in these genetically distinct hosts.